5. Step 2 Elig. (MTX Infusion Elig.): Clinical Performance Status - Patients must have a Lansky score of 50 or greater if ≤ 16 years of age and a Karnofsky score of 50 or greater if they are > 16 years of age to be eligible for enrollment (See Protocol Section 14.1 for Lansky Play-Performance Scale information; See Protocol Section 14.2 for Karnofsky Performance Scale information).